A number of questions on the Intel Virtualization and Software Development Forum have come up on the topic of VT-c, so perhaps it&aposs time for a blog entry on the subject.

Intel Virtualization Technology for Connectivity, or VT-c, is a collection of technologies that improve the performance of network I/O on a virtualized system. VT-c is comprised of two components at the time of this writing: VMDq and VMDc.

VMDc, or Virtual Machine Direct Connect, uses the PCI-SIG standard called SR-IOV to virtualize physical I/O ports of a network controller into multiple virtual I/O ports, and then to map the virtual ports to individual VMs. The result is near-native network I/O performance for VMs which can now make use of direct access.

Users have asked whether VT-c is a hardware or software-based set of performance features. The answer is "yes" and "yes" — in other words, both are required to enable VT-c capabilities. VMDq, case in point, requires the hardware support of particular network interfaces, driver support, and VMM support.